Hi ,I see a lot of DIY answers to a few Cox engine parts and wondered if there are easy solutions for the paper gas tank gaskets and fuel hose on the 049 and 020 engines .??. With out buying them from a vendor in Ca or Canada with shipping. New screws would be nice too for cases and prop. Sourcesanybody or methods to make ??Thanks for any help.Trying to put our collection of Coxes back together that we had as kids ...Steve stevenehlers77@gmail.com

SteveEhlers wrote:Hi ,I see a lot of DIY answers to a few Cox engine parts and wondered if there are easy solutions for the paper gas tank gaskets and fuel hose on the 049 and 020 engines .??. With out buying them from a vendor in Ca or Canada with shipping. New screws would be nice too for cases and prop. Sourcesanybody or methods to make ??Thanks for any help.Trying to put our collection of Coxes back together that we had as kids ...Steve stevenehlers77@gmail.com

Hi Steve! I can tell you that the case-screws for the Cox reed-valve (Bee) .049 engines are 2-56 and the prop-screw for "all" Cox .049/.051 engines is a 5-40. The Cox Pee Wee .020 also uses 2-56 case-screws.. and both; Cox Pee Wee and Tee Dee .020 engines use a 3-48 prop-screw.

These screws aren't easy to source locally.. and they need to be the thread-length/head-style configurations to suit your particular engine. Fuel-lines are easy-enough to replace.. but the gaskets and screws are better-off being sourced from a qualified Cox-engine dealer. If your rebuilding Cox "tanked" engines; such as the .049 "Bee's" or the .020 "Pee Wee".. you'll want to obtain rebuild-kits for "those" engines. They should include a new case-gasket, a venturi-gasket, a new reed and replacement-screws (specify your tank size for the .049 engine.. 5cc or 8cc). If your engines are old-vintage, they will use a wire-clip reed-retainer that seats into the front of the tank. The newer .049 engines utilize a plastic "cap-style" reed-retainer with a flange in the shape of a case-gasket. You'll know which type you have when you disassemble your engines for rebuild. Either type of reed-retainer doesn't ordinarily need to be replaced when rebuilding an engine.. but the "reed" may need replacing if it's bent/creased/deformed.

The reed is thin and fragile.. but may still be useable, so use care when removing/cleaning it. If it's a star-shaped copper reed; be VERY careful with it. The copper reeds are no longer being produced. That said; the available "thicker" Mylar reeds can be substituted.. as long as they "seal" properly. A reed that's "stuck" to its seat because of gummed-up old fuel, should be soaked in solvent for a few days. Place the tank in a small jar of solvent or model-engine fuel.. then try to gently "lift" a corner using a sewing-needle or the point of a #11 hobby-knife blade. Be careful not to scratch the seat behind the reed. Once the reed is removed, clean the seat area using a cotton-swab soaked in solvent or model-engine fuel.. until the seat is clean of any residue.

Many people neglect to replace the "venturi-gasket" when rebuilding a tanked-engine. It's the small round gasket that fits onto the tube at the rear of a tank-bowl and seals against the back-plate. A leaky-seal here can cause problems. "Any" leaks can cause problems with a tanked engine.. so be aware of any fuel leaking around the tank.. and take the necessary measures to correct it.

Maybe this was more information than you needed.. but these tips have helped me to keep my engines running reliably. Good luck!

Roddie, Thanks for your detailed answer. Yea, I know a lot about them along with info you mentioned, but didn't know the screw sizes off hand. I have a friend that owns a Bolt company and I will see if they have anything before I order . Thanks again !Steve

What I'm mostly referring to in my answer is the Cox Bee type reed valve engines with the built-on fuel tank.

Unfortunately, these screws are all slot drives, slip, puncture, and cuss drives, SPC drives. They fit mounting tabs without scratching the tank wall, and they fit tank backplates too. For added safety against cracking or deforming the internal boss of the tank backplates, I believe the #2 washers will fit inside the recess. For final assembly, that washer makes a good seal against air leaks with a little RTV smeared on the underside of it, and under the screw head too. Micro cracks in this area are one of the hair pullers of tanked Cox engines. Many of the maddening problems of erratic running tanked reed engines are pesky air leaks.

Another one is that the threads in the crankcase are not always deep enough, either to maintain a good grip on a screw, or other times it'll give a false impression that a slightly longer screw is tight... when in fact, it's only run out of threads, leaving both the crankcase and backplate leaky. This is the #1 reason you should get a 2-56 plug tap, or flatten the tip of a taper tap. The holes are plenty deep enough, just not threaded all the way down. This makes the backplate feel tight before the screws are actually in all the way. I've extended the threads up to 5-8 turns deeper on some engines.

There are many other reasons for performance killing air and fuel leaks there too. The flat washer Roddie mentions sealing the venturi tube to the backplate's air inlet will cause it to possibly run well at first and then sputter and change speed when the fuel level drops and uncovers this seal. The head pressure goes haywire. Though at first glance it looks like a worn out flattened o-ring, it's not toroidal and if you try to force a small o-ring to work, it may deform the already super bitchy backplate. Especially the plastic ones. People have made replacements with varying success... silicon fuel line slices, latex surgical tube lots of experiments have been done. But give it a try, maybe you'll nail it. Maybe a thin wall bicycle innertube. Probably been done.

Tank to crankcase gaskets; I've done it with heavy duty aluminum foil and RTV. RTV alone works too, but it's just a mess if you have to take it apart in the field for a quick fix of whatever else starts leaking. Paper or some other gasket material from the auto parts store might be a good bet.

You can get pretty crafty with internal pickup tubes. Aluminum secured with a tight collar of fuel tube to affix it to the nipple. Make sure the pickup opening is sliced at an angle so it doesn't suck up to the side.

Copper head gaskets, buy 'em. Buy a sack full of them. eBay sources may vary in thickness and metallurgy, but you can work around that and they'll usually be fine. Norvel .049 and .061s have the same ID/OD, but I haven't compared the thickness. Old ones can be annealed with a not too aggressive torch to bring back their malleability, but won't fatten them up after they're crushed and thinner. But it will help prevent working loose during a run I watched one of our members who's name I won't mention vaporize a Tee Dee .010 gasket in about a half a second with my propane torch, Lol. Personally, I like to support Cox International and Ex Model Engines(Bernie and Matt) and buy things like this from them. They have both been very good to us with high-class customer service, not hesitating to work together for our sake, and quite frankly we need each other. So browse their sites and balance frustrating trouble and time spent with a few bucks. Start a Cuss Jar, Lol, damn, I just thought of that. Only put money in it when your cussing is directed at a failed fix for a Cox Engine.

Glow plugs; Both of them sell the interchangeable Merlin drop-in and clamp ring head types. Unless you're a purist and only want OEM parts, these are the best replacements for low and high compression. They need more washers to tame the compression, even in the high comp. applications.* Clamp ring head with glow plug - https://coxengines.ca/cox-.049-glow-plug-adapter-insert-style.html* Replacement glow plugs can be bought for $5.95. The spring loaded sub-c pocket glow igniters like many of us use on our stunt(and other standard plug) engines will fit these too.

Reeds can be made out of many materials. Old floppy disk material used to be popular. I have not tried it, I just buy a little sack full of the Mylar(Not Teflon) oval reeds. Depending on the type of reed retainer, some shapes and thicknesses work better than others. I have some medicine patch peel-off plastic backing that I think would work well, but again, never tried it.

Starter springs are a must for me. I love the anti-reverse cam-ring type starter spring. And stay far away from old plastic props. Don't let anybody tell you that boiling them will rejuvenate them either.

Check out the Bulk items for sale your going to need them sooner or later http://www.exmodelengines.com/home.php?cat=264 Reeds are easy to cut from tracing a oval one with a marker .005 thick cheap binders that are made of Mylar , Walmart , Dollar store ect..

Hint#2 pay close attention above to what rusty suggested with THIS ADDITIONAL hint:

Rusty was saying that the Cox screw holes in the Crank Case are not tapped deep enough and some Back Plate screws bottom out and never get tight enough to seal the tank....and that is a very true condition.

What he forgot to tell you is a hint he offered to us was to properly LAP The Back of the Crank Case on a Flat Glass ( or any other real flat surface) with oiled 400/600/800 grit paper... This step removes the slightly raised burrs from the screw holes drilling operation and also gets the gasket surface very flat and true

Yep, Fred's right. I also didn't mention sealing the tongue and groove fit between the edge of the tank and tank-backplate interface. Some people wet a piece of Dacron flying line and press it into the groove to help seal it. Personally I have had success with a tiny amount of RTV. There are different types of Permatex and other RTV sealers, be sure and get an oil proof type. There's also anaerobic, but I don't remember all the preferred details without looking at what's in my shop fridge, which I'm not near at the moment. I used the term "final assembly" in my first post... that's a sort of laughable term for a tanked Bee. But they sure do run well when you master them.

If you can get yourself a Cox Medallion or two, wash them out, bolt them up and never look back. They will run first time every time all day long. A Tee Dee engine is also a highly dependable and more powerful option, but needs a little more finesse in the fuel-draw department.

Rusty

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Don't Panic!...and never Ever think about how good you are at something...while you're doing it!

Thanks to everybody with your info. I thought this note went through already. I plan to go through the pile of parts we had as kids,clean and pick the best to put together and install on some Firebabys that I will give my brothers. I will try to send some pics when I get some together. Again thanks for the help on this forum.Steve